This invention relates to a locking device for trailer kingpins. In the conventional trailer construction, the trailer chassis is provided with a kingpin depending vertically therefrom, said kingpin having a recess, or groove, disposed circumferentially therein. The trailer is typically provided with a skid plate having an opening through which the trailer kingpin extends, and the trailer is coupled to the tractor by backing the tractor up to the kingpin which is engaged by a complementary unit, or fifth wheel, on said tractor. The trailer-tractor combination is commonly used for the transportation of freight. When the destination is reached, the trailer is usually uncoupled from its tractor to await the unloading of the cargo. It is also frequently desirable to uncouple the tractor from the trailer for the convenience of the driver before and during loading as well as after unloading. It is frequently necessary to leave the trailer unattended on occasions such as those mentioned above, with the result that highjackers, on constant lookout for such situations, couple the trailer to another tractor and drive off with the cargo.
The annual loss sustained by shippers and insurance companies due to highjacking of trailers is very substantial. Apart from the monetary injury suffered, the trucking concern whose trailer has been highjacked often finds it difficult to obtain new insurance, and without adequate insurance, soon finds itself in financial difficulty, as few shippers will entrust their cargo to an uninsured trucking concern.
To obviate the shipping hazards mentioned above, as well as to reduce insurance costs to trucking companies, there have been devised a number of locking devices which, when fitted to a trailer kingpin, provide an effective safeguard against coupling the trailer to a tractor by an unauthorized person. A typical locking device for trailer kingpins is described in U.S. Pat. No. 2,755,655, issued July 24, 1956. The locking device described therein is a casing which encircles the kingpin and is locked thereto by a slidable locking bar within an aperture in said casing, the locking bar having a key-actuated lock unit disposed therein. When the locking bar is in the locked position, its inner end enters the recess, or groove, of the trailer kingpin and its outer end is flush with the outer wall of the casing. However, if a careless driver attempts to couple a tractor to a trailer having such a locking device in place, the fifth wheel of the tractor will strike the locking device with sufficient force to cause deformation and burring to the metal. If the damage so inflicted occurs in the area of the locking bar and the key-actuated lock unit, the locking bar or the lock unit may be damaged. In addition, the opening to the aperture containing the locking bar may be burred so that the locking bar will no longer slide to allow the locking device to be disengaged from the kingpin.